1. Field of the Invention
This invention relates to a digital-to-analog converter for converting a digital signal to an analog signal, and more particularly, to a digital-to-analog converter suitable for digital audio devices or the like.
2. Description of the Related Art
For a digital-to-analog (D/A) converter used in digital audio devices or the like, it is necessary to attain a monotonic increase in a D/A conversion output (that is, linear characteristic of D/A conversion) while reducing the size of the D/A converter. To meet the requirement, a digital-to-analog (D/A) converter has been used which employs capacitor arrays and resistor segments as described in U.S. Pat. No. 4,200,863, for example.
The D/A converter described in this patent includes capacitor arrays (C1 to C256) and resistor segments (R1 to R16) to constitute an A/D converter for converting analog input signal Vin to a 12-bit digital signal, as is shown in FIG. 4. It also has a function as a D/A converter for converting a 12-bit digital signal to an analog signal.
That is, when the A/D converter shown in FIG. 4 is operated as a D/A converter, it converts the upper 8 bits of a digital signal by using 8-bit capacitor arrays which are binary-weighted and converts the lower 4 bits by using resistor segments R1 to R16.
In the case where such a D/A converter is used to D/A convert a digital signal, no serious problem arises if the bit number of units of the digital signal is small. However, in the case of an IC for D/A converting a digital signal having a large number of bits, there is a problem because the total area of the capacitors required is greatly increased and the number of resistors used is increased significantly.
For example, in the case where the D/A converter is used for 16-bit D/A conversion which is conventionally utilized in digital audio devices, and upper and lower 8 bits are D/A converted by using the capacitor arrays and resistor segments, respectively, then total capacitor area Cs required on the upper bit side can be expressed as follows: ##EQU1## where C is a minimum capacitor area.
Likewise, the number Rs of resistors required on the lower bit side can be expressed as follows: EQU Rs=2.sup.8 =256R
Thus, when a 16-bit digital signal is converted to an analog signal, a total of 256 capacitors C and 256 resistors R are needed, making the IC chip area remarkably large. Furthermore, such an increase in the number of elements leads to a high cost of the D/A converter.